Fast-freeze systems for processing food products, such as meats, fruits, vegetables, etc. have been extensively used in the food industry for many years in order to preserve and store for economical year-round use seasonal foods and those whose production is subject to variables of economic conditions. In addition to storage, an important commercial consideration requires that the natural flavor, juices, nutrients, color and appearance of the foods be preserved to the extent practically possible. In this respect, high rate of freezing is an important consideration.
The prior art systems generally available for this purpose have significant disadvantages that the present invention aims to overcome; for example, in the well-known cold air-blast system, the freezing process is not sufficiently fast for avoiding some dehydration, with corresponding decrease in quality of the frozen product. Spraying of liquid carbon dioxide into the freezing compartment where it is vaporized and circulated around the food products, has also been used and found in some instances to lack sufficiently high freezing rate for desired production. In another known system wherein freezing takes place within a so-called liquid-nitrogen tunnel, the operation is generally more expensive due to the cost of the storage and transfer piping required to handle it; also, production time may be lost while waiting for cool-down of the tunnel. Other freezing systems using nitrogen in lieu of carbon dioxide spray have been tried but have not to the best of applicant's knowledge been successful for obtaining satisfactory freezing due in general to improper techniques in handling the nitrogen spray.
The present invention is concerned with a highly efficient and high-speed freezing system that utilizes liquid nitrogen spray to advantage, and is economical both in equipment cost, operating cost and system maintenance.